The science of genetics has taken a keen interest in the identification of human individualization and genetic relationships between individuals. Each individual has hereditary material (DNA, "nucleotides") which is unique to that individual and hereditary material which is related to that of others. Procedures have been developed which are based on identification and characterization of changes in DNAs, which are changes in DNA (DNA polymorphisms) due to nucleotide substitution, insertion, or deletion within the chains of DNAs.
In the field of forensic medicine, for example, there is a keen interest in such polymorphisms for identification purposes. Forensic geneticist have developed many techniques to compare homologous segments of DNA to determine if the segments are identical or if they differ in one or more nucleotides. Practical applications of these techniques relate to fields other than forensic medicine, for example, genetic disease diagnosis and human genome mapping.
At the present time in this art, the most accurate and informative way to compare DNA segments requires a method which provides the complete nucleotide sequence for each DNA segment. Particular techniques have been developed for determining actual sequences in order to study mutation in human genes. See, for example, Proc. Natl. Acad. Sci. U.S.A. 85, 544-548 (1988) and Nature 330, 384-386 (1987). However, because of the extensive amounts of time and high costs to determine, interpret, and compare sequence information, presently it is not practical to use extensive sequencing for compare more than just a few DNA segments.
In genetic mapping, the most frequently used screening for DNA polymorphisms arising from mutations consist of digesting the DNA strand with restriction endonucleases and analyzing the resulting fragments by means of Southern blots. See Am. J. Hum. Genet. 32, 314-331 (1980) or Sci. Am. 258, 40-48 (1988). Since mutations often occur randomly they may affect the recognition sequence of the endonuclease and preclude the enzymatic cleavage at that cite. Restriction fragment length polymorphism mappings (RFLPS) are based on changes at the restriction site. They are accurate but not very informative (PIC [0.3). The major problem with RFLPs is the inability of a test to detect changes that do not affect cleavage with a restriction endonuclease. As in many of the test methods in the DNA art, the methods used to detect RFLPs are very labor intensive and expensive, especially the techniques which includes Southern blot analysis.
Another technique for detecting specific mutations in particular DNA segment involves hybridizing DNA segments which are being analyzed (target DNA) with a complimentary, labeled oligonucleotide probe. See Nucl. Acids Res. 9, 879-894 (1981). Since DNA duplexes containing even a single base pair mismatch exhibit high thermal instability, the differential melting temperature can be used to distinguish target DNAs that are perfectly complimentary to the probe from target DNAs that only differ by a single nucleotide. This method has been adapted to detect the presence or absence of a specific restriction site, U.S. Pat. No. 4,683,194. The method involves using an end-labeled oligonucleotide probe spanning a restriction site which is hybridized to a target DNA. The hybridized duplex of DNA is then incubated with the restriction enzyme appropriate for that site. Reformed restriction sites will be cleaved by digestion in the pair of duplexes between the probe and target by using the restriction endonuclease. The specific restriction site is present in the target DNA if shortened probe molecules are detected.
Another process for studying differences in DNA structure is the primer extension process which consists of hybridizing a labeled oligonucleotide primer to a template RNA or DNA and then using a DNA polymerase and deoxynucleoside triphosphates to extend the primer to the 5' end of the template. Resolution of the labeled primer extension product is then done by fractionating on the basis of size, e.g., by electrophoresis via a denaturing polyacrylamide gel. This process is often used to compare homologous DNA segments and to detect differences due to nucleotide insertion or deletion. Differences due to nucleotide substitution are not detected since size is the sole criterion used to characterize the primer extension product.
Another process exploits the fact that the incorporation of some nucleotide analogs into DNA causes an incremental shift of mobility when the DNA is subjected to a size fractionation process, such as electrophoresis. Nucleotide analogs can be used to identify changes since they can cause an electrophoretic mobility shift. See, U.S. Pat. No. 4,879,214.
Unfortunately, the above techniques used for identification of polymorphisms are either not very informative or take a long period of time to perform. For example, techniques which identify changes in individual nucleotides on a particular DNA strand often take at least three to four days to perform. Accordingly, such tests are very labor intensive and expensive to perform.
Further, subtle genetic differences among related individuals regarding nucleotides which are substituted in the DNA chains are difficult to detect. VNTR's or Jeffrey's probes (which the FBI is using to test and identify DNA chains) are very informative but labor intensive, in distinction to microsatellites as our which are equally informative PCR based polymormismic.
The use of certain nucleotide repeat polymorphisms for identifying or comparing DNA segments have been described by Weber & May 89 Am Hum Genet 44:388, Litt & Luthy '89 Am) Hum Genet 44:397). However the particular polymorphism genetic segments and primers used to identify the polymorphisms (for identification and comparison purposes) of the present invention have not been previously known or suspected.
Accordingly, there a need in this art for a rapid, simple, inexpensive and accurate technique having a very high resolution value to determine relationships between individuals and differences in degree of relationships. Also, there is a need in the art for a very accurate genetic relationship test procedure which uses very small amounts of an original DNA sample, yet produces very accurate results. This is particularly true in the forensic medicine area and criminology, since often times very small samples of DNA are available for testing.